1. Field of the Invention
The present invention relates to a coating film forming apparatus and coating film forming method for forming a coating film, such as a resist film, on a substrate before a light exposure process. Particularly, the present invention relates to a coating film forming apparatus and coating film forming method suitable for a double patterning technique.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, photolithography techniques are used for forming circuit patterns on semiconductor wafers (which will be simply referred to as “wafer”, hereinafter), which are treated as target substrates. Where a circuit pattern is formed by use of photolithography, the process steps are performed, as follows. Specifically, a resist liquid is first applied to a wafer to form a resist film. Then, the resist film is irradiated with light to perform light exposure on the resist film in accordance with the circuit pattern. Then, the resist film is subjected to a developing process.
In recent years, the integration degree of semiconductor devices becomes increasingly higher to improve the operation speed and so forth. Accordingly, photolithography techniques are required to increase the miniaturization level of circuit patterns formed on wafers. As a photolithography technique for realizing a high resolution of a 45-nm node level, there has been proposed the following immersion light exposure (for example, see U.S. Patent Application Publication No. US 2006/0231206 A1). In this immersion light exposure, a light exposure liquid, such as purified water, having a refractive index higher than air is supplied between the wafer and light exposure projection lens. The wavelength of light radiated from the projection lens is shortened by means of the refractive index of the light exposure liquid, so that the line width obtained by the light exposure is decreased. Further, there has been proposed a double patterning technique for forming micro-patterns by performing patterning operations twice. Combinations of an immersion light exposure technique with a double patterning technique have been studied.
In the double patterning technique, light exposure needs to be performed twice before etching, so particles generated before the light exposure can be easily carried into the light exposure apparatus. If particles are present on the back surface of a wafer, defocusing may occur on portions with the particles during the light exposure process. Conventionally, defocusing is caused only by relatively large particles. However, along with an increase in miniaturization level of technical nodes, defocusing can be caused by smaller particles. Thus, the presence of particles on the back surface of a wafer is becoming a non-negligible problem. Further, along with an increase in miniaturization level, the number of steps in photolithography has become larger and thereby increased the risk of particles being deposited on the back surface of a wafer. Accordingly, it is now more important than ever to prevent particles from being carried into a light exposure apparatus from a coating film forming apparatus for a resist film or the like.